var foo = function () {
    var a = 3, b = 5;

    var bar = function () {
        var b = 7, c = 11;
        console.log('1', a, b, c); // a = 3, b = 7, c = 11
        a += b + c;
        console.log('2', a, b, c); // a = 21, b = 7, c = 11
    };
    console.log('3', a, b); // a = 3, b = 5, c没有定义
    bar();
    console.log('4', a, b);// a = 21, b = 5, c没有定义
};
foo();
